Quantum mechanical calculations are performed on a series of silicon radical defects. These are the v Si O3-xNx, up arrow Si N3-xSix, and up arrow Si Si3-xOx defects, where x takes on values between 0 and 3. The defects under study constitute a central silicon radical, v Si, with differing first-nearest-neighbor substitution, as may be found at a Si/SiOxNy interface. These first-nearest neighbor atoms are connected to the silicon radical via three single covalent bonds, denoted as "=". A hybrid defect, up arrow Si ONSi, is also included. Calculations are performed on gas-phase-like cluster models, as well as more-constrained hybrid quantum and molecular mechanical ( QM/MM) models. The isotropic hyperfine coupling constants of these defects are calculated via density functional theory ( DFT). Trends in these calculated hyperfines are consistent between the different models utilized. Analysis of the electronic structure and geometries of defects correlate well with trends in the electronegativity of the first-nearest-neighbor atoms. Changes in radical hybridization, induced by changes in the first-nearest-neighbor composition, are the primary factor that affects the calculated hyperfines. Furthermore, comparisons to experimental results are encouraging. Agreement is found between experiments on amorphous to crystalline materials.